Using data from the German Socio-Economic Panel, we undertake a simultaneous assessment of the importance of factors that are individually found to be significant for the adoption of renewable energy systems by households but are not yet tested jointly. These are sociodemographic and housing characteristics, environmental concern, personality traits, and economic factors; i.e. the expected costs of and revenues from the investment. Our results suggest that household decisions to invest in photovoltaic systems and solar thermal facilities are mainly driven by economic factors. Taking account of sociodemographic and housing characteristics, environmental concern, or personality traits has comparatively little relevance, while the quantitative nexus between the decision to invest and returns on the investment is robust to their inclusion.